DevAuthBackend: Improve the query for dev users.

This changes the query for DevAuthBackend so that the shakespearian
users are not omitted while limiting the number of extra users to be
rendered to something reasonable.

Fixes: #3578.

zerver/views/auth.py

@@ -325,6 +325,19 @@ def log_into_subdomain(request):
     return login_or_register_remote_user(request, email_address, user_profile,
                                          full_name, invalid_subdomain)
 
+def get_dev_users(extra_users_count=10):
+    # type: (Optional[int]) -> List[UserProfile]
+    # Development environments usually have only a few users, but
+    # it still makes sense to limit how many extra users we render to
+    # support performance testing with DevAuthBackend.
+    users_query = UserProfile.objects.select_related().filter(is_bot=False, is_active=True)
+    shakespearian_users = users_query.exclude(email__startswith='extrauser').order_by('email')
+    extra_users = users_query.filter(email__startswith='extrauser').order_by('email')
+    # Limit the number of extra users we offer by default
+    extra_users = extra_users[0:extra_users_count]
+    users = list(shakespearian_users) + list(extra_users)
+    return users
+
 def login_page(request, **kwargs):
     # type: (HttpRequest, **Any) -> HttpResponse
     if request.user.is_authenticated():
@@ -335,12 +348,7 @@ def login_page(request, **kwargs):
 
     extra_context = kwargs.pop('extra_context', {})
     if dev_auth_enabled():
-        # Development environments usually have only a few users, but
-        # it still makes sense to limit how many users we render to
-        # support performance testing with DevAuthBackend.
-        MAX_DEV_BACKEND_USERS = 100
-        users_query = UserProfile.objects.select_related().filter(is_bot=False, is_active=True)
-        users = users_query.order_by('email')[0:MAX_DEV_BACKEND_USERS]
+        users = get_dev_users()
         extra_context['direct_admins'] = [u.email for u in users if u.is_realm_admin]
         extra_context['direct_users'] = [
             u.email for u in users
@@ -410,9 +418,7 @@ def api_dev_get_emails(request):
     # type: (HttpRequest) -> HttpResponse
     if not dev_auth_enabled() or settings.PRODUCTION:
         return json_error(_("Dev environment not enabled."))
-    MAX_DEV_BACKEND_USERS = 100 # type: int
-    users_query = UserProfile.objects.select_related().filter(is_bot=False, is_active=True)
-    users = users_query.order_by('email')[0:MAX_DEV_BACKEND_USERS]
+    users = get_dev_users()
     return json_success(dict(direct_admins=[u.email for u in users if u.is_realm_admin],
                              direct_users=[u.email for u in users if not u.is_realm_admin]))